@property (strong, nonatomic) NSMutableString *authCodeStr;//验证码字符串
- (void)getAuthcode;

//背景随机颜色
#define kRandomColorAL  [UIColor colorWithRed:arc4random() % 256 / 256.0 green:arc4random() % 256 / 256.0 blue:arc4random() % 256 / 256.0 alpha:0.5];
//干扰线随机颜色
#define kRandomColor  [UIColor colorWithRed:arc4random() % 256 / 256.0 green:arc4random() % 256 / 256.0 blue:arc4random() % 256 / 256.0 alpha:1];
//干扰线数量
#define kLineCount 4
//干扰线宽度
#define kLineWidth 1.0
//验证码数量
#define kCharCount 4
//验证码大小
#define kFontSize (arc4random() % 5 + 20)

- (instancetype)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self)
    {
        self.layer.cornerRadius = 5.0f;
        self.layer.masksToBounds = YES;
        self.backgroundColor = kRandomColor;
        
        [self getAuthcode];//获得随机验证码
    }
    return self;
}

#pragma mark 获得随机验证码
- (void)getAuthcode
{
    //字符串素材
    _dataArray = [[NSArray alloc] initWithObjects:@"0",@"1",@"2",@"3",@"4",@"5",@"6",@"7",@"8",@"9",@"A",@"B",@"C",@"D",@"E",@"F",@"G",@"H",@"I",@"J",@"K",@"L",@"M",@"N",@"O",@"P",@"Q",@"R",@"S",@"T",@"U",@"V",@"W",@"X",@"Y",@"Z",@"a",@"b",@"c",@"d",@"e",@"f",@"g",@"h",@"i",@"j",@"k",@"l",@"m",@"n",@"o",@"p",@"q",@"r",@"s",@"t",@"u",@"v",@"w",@"x",@"y",@"z",nil];
    
    _authCodeStr = [[NSMutableString alloc] initWithCapacity:kCharCount];
    //随机从数组中选取需要个数的字符串，拼接为验证码字符串
    for (int i = 0; i < kCharCount; i++)
    {
        NSInteger index = arc4random() % (_dataArray.count-1);
        NSString *tempStr = [_dataArray objectAtIndex:index];
        _authCodeStr = (NSMutableString *)[_authCodeStr stringByAppendingString:tempStr];
    }
}

#pragma mark 点击界面切换验证码
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    [self getAuthcode];
    
    //setNeedsDisplay调用drawRect方法来实现view的绘制
    [self setNeedsDisplay];
}

#pragma mark 绘制
- (void)drawRect:(CGRect)rect
{
    [super drawRect:rect];
    
    //设置随机背景颜色
    self.backgroundColor = kRandomColorAL;
    
    //根据要显示的验证码字符串，根据长度，计算每个字符串显示的位置
    NSString *text = [NSString stringWithFormat:@"%@",_authCodeStr];
    
    CGSize cSize = [@"A" sizeWithAttributes:@{NSFontAttributeName:[UIFont systemFontOfSize:20]}];
    
    int width = rect.size.width/text.length - cSize.width;
    int height = rect.size.height - cSize.height;
    
    CGPoint point;
    
    //依次绘制每一个字符,可以设置显示的每个字符的字体大小、颜色、样式等
    float pX,pY;
    for ( int i = 0; i<text.length; i++)
    {
        pX = arc4random() % width + rect.size.width/text.length * i;
        pY = arc4random() % height;
        point = CGPointMake(pX, pY);
        
        unichar c = [text characterAtIndex:i];
        NSString *textC = [NSString stringWithFormat:@"%C", c];
        UIFontDescriptor *attributeFontDescriptor = [UIFontDescriptor fontDescriptorWithFontAttributes:
                                                     @{UIFontDescriptorFamilyAttribute: @"Marion",
                                                       UIFontDescriptorNameAttribute:@"HanziPenSC-W3",
                                                       UIFontDescriptorSizeAttribute: @40.0,
                                                       UIFontDescriptorMatrixAttribute:[NSValue valueWithCGAffineTransform:CGAffineTransformMakeRotation(M_1_PI*(arc4random() % 2 ))
                                                                                        ]}];
        UIFont * font = [UIFont fontWithDescriptor:attributeFontDescriptor size:kFontSize];
        UIColor *color = kRandomColor;
        [textC drawAtPoint:point withAttributes:@{NSFontAttributeName:font,NSForegroundColorAttributeName:color}];
        
    }
    
    
    //调用drawRect：之前，系统会向栈中压入一个CGContextRef，调用UIGraphicsGetCurrentContext()会取栈顶的CGContextRef
    CGContextRef context = UIGraphicsGetCurrentContext();
    //设置线条宽度
    CGContextSetLineWidth(context, kLineWidth);
    
    //绘制干扰线
    for (int i = 0; i < kLineCount; i++)
    {
        UIColor *color = kRandomColor;
        CGContextSetStrokeColorWithColor(context, color.CGColor);//设置线条填充色
        
        //设置线的起点
        pX = arc4random() % (int)rect.size.width;
        pY = arc4random() % (int)rect.size.height;
        CGContextMoveToPoint(context, pX, pY);
        //设置线终点
        pX = arc4random() % (int)rect.size.width;
        pY = arc4random() % (int)rect.size.height;
        CGContextAddLineToPoint(context, pX, pY);
        //画线
        CGContextStrokePath(context);
    }
}

@property (nonatomic, strong) MaxAuthCodeView * authcodeImage;/**< 验证码视图*/

self.authcodeImage = [[MaxAuthCodeView alloc] initWithFrame:CGRectMake(50, 100, 120, 60)];
    [self.view addSubview:self.authcodeImage];
    [self.authcodeImage getAuthcode];

NSLog(@"%@",self.authcodeImage.authCodeStr);